-- Introduction to database principles Maoying Wu March 25, 2013 Chapter 4: Advanced SQL (1)

Outline SQL: Data Types Integrity Constraints

Built-in Data Types date: Dates, containing 4-digit year, month and date date ‘ ’ time: Time of day, in hours, minutes and seconds time ’09:00:30’’09:00:30.75’ timestamp: date plus time of day timestamp ‘ :30:127.5’ interval: period of time interval ‘1’day The difference between 2 date / time / timestamp values interval values can be added to date / time / timestamp values

Built-in Data Types in SQL (Cont.) extract(year from r.starttime) extract values of individual fields from date/time/timestamp cast as date/time cast string data to date/time/timestamp

User-Defined Types CREATE TYPE construct in SQL creates a user-defined type CREATE TYPE dollars AS numeric(12,2) FINAL CREATE DOMAIN construct in SQL-92 creates user- defined domain type CREATE DOMAIN person_name char(20) NOT NULL Types and domains are similar. Domains can have constraints, such as NOT NULL, specified on them.

Domain Constraints Most elementary form of integrity constraint Create domains CREATE DOMAIN Dollar numeric(12,2); CREATE DOMAIN Pound numeric(12,2); We cannot assign or compare values of different domains however, we can use cast to convert (CAST r.A as Pound)

Large-object types Large object include photos, videos, CAD files, etc. blob: binary large object clob: character large object When a query returns a large object, a pointer is returned rather than the large object itself

Integrity constraints Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency A checking account must be of balance more than $10, The lowest salary for a bank employee must be $10.00 an hour A customer must have a non-null phone number

Constraints on a single relation NOT NULL PRIMARY KEY UNIQUE CHECK(p), where p is a predicate

NOT NULL branch_name char(15) NOT NULL CREATE DOMAIN Dollar numeric(12,2) NOT NULL

UNIQUE UNIQUE (A 1, A 2, …, A m ) UIQUE statements specifies that the attributes (A1, A2, …, Am) form a candidate key NULL values are allow for candidate keys (in contrast to primary keys)

ENTITY INTEGRITY PRIMARY KEY must be NOT NULL

CHECK(p) check(p), where p is a predicate CREATE TABLE branch (branch_namechar(15), branch_citychar(30), assetsinteger, primary key (branch_name), check (assets >= 0); CREATE DOMAIN hourly_wage numeric(5,2) [constraint value_test ] check (value >= 10.00);

Referential Integrity create table customer (customer_name char(20), customer_street char(30), customer_city char(30), primary key (customer_name )) create table branch (branch_name char(15), branch_city char(30), assets numeric(12,2), pr create table account (account_number char(10), branch_name char(15), balance integer, primary key (account_number), foreign key (branch_name) references branch ) create table depositor (customer_name char(20), account_number char(10), primary key (customer_name, account_number), foreign key (account_number ) references account, foreign key (customer_name ) references customer );

Assertions An assertion is a predicate An assertion in SQL takes the form create assertion check When an assertion is made, the system tests it for validity, and tests it against every update Asserting for all X, P(X) is achieved in a round-about fashion using not exists X such that not P(X)

Assertion: Example Every loan has at least one borrower who maintains an account with a minimum balance of $ create assertion balance_constraint check (not exists ( select * from loan where not exists ( select * from borrower, depositor, account where loan.loan_number = borrower.loan_number and borrower.customer_name = depositor.customer_name and depositor.account_number = account.account_number and account.balance >= 1000)))